YAOUNDE (Reuters) - Cameroonian President Paul Biya secured approval from lawmakers on Tuesday to delay parliamentary and local elections until 2026, a move opposition parties fear could make it harder for them to mount a challenge in next year's presidential election.

Lawmakers in Biya's Cameroon People's Democratic Movement have a majority in the National Assembly and voted in favour of the bill to extend their mandate by a year to March 2026.

As a result, legislative elections - and municipal elections usually twinned with them - will take place after the 2025 presidential poll.

The delay was needed to "lighten the electoral calendar" as the central African nation originally had four polls - including regional council polls - scheduled for next year, said François Wakata Bolvine, the presidency's minister delegate in charge of relations with the assemblies.

Biya, 91, is one of Africa's longest-serving presidents. He took over in 1982 from President Ahmadou Ahidjo and has won a series of elections, most recently a 2018 vote that his opponents called fraudulent.

Joshua Osih, opposition lawmaker and chairman of the Social Democratic Front (SDF) party, told a press conference delaying the elections was completely undemocratic.

"The SDF is strongly opposed," he said.

Many in the opposition fear the extension could weaken the challenge to Biya, because holding legislative and municipal elections next year could have given them momentum ahead of a presidential election scheduled for October 2025.

The electoral code stipulates that a presidential candidate can only be nominated by a political party that has representation in the National Assembly, Senate, Regional Council or Municipal Council, or via a recommendation from at least 300 dignitaries.

Maurice Kamto, Biya's main challenger in 2018, does not have such representation as his party boycotted the last municipal and legislative elections over the lack of electoral reforms.

(Editing by Alessandra Prentice and Mark Potter)

By Amindeh Blaise Atabong